There are approximately five million Americans suffering from heart failure. About 550,000 new cases are diagnosed every year and, at any given time, there are nearly a half million Americans living with advanced stage heart failure (e.g., stage III or stage IV heart failure). Approximately 280,000 people die from heart failure each year in the United States.
In heart failure, the left ventricle does not adequately contract to force the blood volume to the systemic circulation. Only a fraction of this volume (usually less than 35%) is ejected, which means that the rest of the volume remains in the ventricle causing it to dilate improperly. Starling's law of the heart states that the greater the volume of blood entering the heart during diastole (end-diastolic volume), the greater the volume of blood ejected during systole (stroke volume). Like a rubber band, the further the heart is stretched the greater is the recoil. However, this works only up to a certain point. When the heart muscles are weakened from infarction or infection, wall tension of the heart does not allow it to expand further to accommodate increase in its radius (Law of Laplace), which explains heart failure.
While heart failure can be treated medically in most cases, once the problem has reached advanced stages, medication becomes less or not at all effective. Medical devices have been used safely and effectively to assist the failing heart and the circulation. There are many assist devices already available, including total artificial hearts (TAH) and ventricular assist devices (VADs). However, in about a third of failing hearts with these devices, total recovery is achieved only by patients who are 40 years old or younger, with a non-ischemic heart as the cause of failure, and, even then, a full recovery is only possible within the first six months. The rest of such patients typically need a heart transplant to survive. Some 60,000 end-stage heart failure patients in the United States need such heart transplants, but only about 2,100 are available every year. VADs and TAH will continue to play a role as temporary circulatory support, as will bridge-to-heart transplantation or destination therapy, due to the shortage of organs available for use as transplants.
There are various forms of VADs, driven by either pulsatile or continuous rotary pumps. Although approved for clinical uses, presently available designs are still prone to serious complications such as infection, bleeding and stroke. No device has been designed that would obviate the need for anticoagulation, which is essential for these devices. Excessive anticoagulation causes bleeding while inadequate anticoagulation can lead to strokes. While medical technology has progressed with the use in the past fifty years of Intra-aortic Balloon Pumps (IABP), aside from indirectly improving remaining heart function by increasing coronary perfusion during diastole and reducing afterload during systole, it has also proven that anticoagulation may not be necessary during circulatory support where interface between patient and device is limited.